Iran's hardline regime has warned the leaders of the post-election protests that they are 'worthy of execution'.

Ayatollah Ahmad Khatami, a member of the clerical leadership, used the platform of Friday prayers at Tehran University to level charges that the regimes opponents were "rioting" in defiance of God's will.

Those arrested should be punished harshly, he said, while their leaders could face the death penalty as enemies of the Islamic Republic.

Iran's regime strengthened its stance in the absence of mass demonstrations, which have come to an end after a brutal police and militia response led to the deaths of dozens of people.

Tehran's defiance was challenged by President Barack Obama on Friday and by G8 foreign ministers, including David Miliband, meeting in Italy, who condemned Iran's harsh repression of the pro-democracy demonstrations since the June 12 election was handed to Mahmoud Ahmadinejad, the incumbent president, amid allegations of massive rigging.

In a strong attack on the strident comments from Iran's leaders, Mr Obama heaped praise on the protesters and dismissed as "not serious" Mr Ahmadinejad's demand this week for an apology for what he claimed was US interference in the election. He admitted that his hopes for a post-election overture to Tehran had been hurt.

Related Articles

"There is no doubt that any direct dialogue or diplomacy with Iran is going to be affected by the events of the last several weeks," he said.

Praising the protesters, he said: "Their bravery in the face of brutality is a testament to their enduring pursuit of justice. The violence perpetrated against them is outrageous."

The US president delivered his first specific boost for Mir-Hossein Mousavi, the rival presidential candidate who has called for the vote to be annulled. “Mousavi has shown to have captured the imagination or the spirit of forces within Iran that were interested in opening up,” he said.

The remark sought to clarify what many view as Mr Obama’s biggest misstep — saying last week in a television interview that there may not be much difference between Mr Ahmadinejad and Mr Mousavi.

Mr Obama also reminded the world of the urgency of stopping Iran's pursuit of a nuclear weapons programme.

"Iran's possession of nuclear weapons will trigger an arms race in the Middle East that would be bad ... for the security of the entire region," he said.

"So even as we clearly speak out in a unified voice in opposition to the violence that's taken place in Iran, we also have to be steady in recognising that the prospect of Iran with a nuclear weapon is a big problem."

A statement from the G8 meeting in Trieste, which brought together the top global economies, including China and Russia, said that the member nations "deplored" the violence meted out by the regime.

The extent of Iran's growing international isolation was demonstrated by harsh remarks by Russia's foreign minister, Sergei Lavrov. "We naturally express our most serious concern about the use of force and the death of civilians," he said.

Mr Lavrov had previously congratulated Mr Ahmadinejad on his re-election.

Ayatollah Khatami is a member of the Assembly of Experts, the 85-member council of clerics that split in the aftermath of the election after its chairman, the former president Hashemi Rafsanjani, rejected efforts to fix the election.

Ayatollah Khatami proclaimed the protests had been mohareb, an Islamic offence that means waging war against God. The punishment for people convicted as mohareb is execution under Iran's sharia legal code.

While clashes on the streets have died away, Iranians continue to demonstrate sympathy for Mr Mousavi.

Thousands released green balloons into the Tehran skies at 1pm. Many were inscribed with a tribute to Neda Agha Soltan, the woman whose death from a gunshot wound was posted on the internet last week: "Neda you will always remain in our hearts."

Mr Mousavi said he was determined to keep challenging the election results despite pressure to stop. "A major rigging has happened," his wrote on his website. "I am prepared to prove that those behind the rigging are responsible for the bloodshed."

He called on his supporters to continue "legal" protests and said restrictions on the opposition could lead to more violence.

Mr Obama's comments on the nuclear issue reflected the efforts of Western diplomats, who are formulating a new approach to negotiations over Iran's suspected pursuit of a bomb through uranium enrichment have been thrown into limbo by events on the streets.

The imperative of forging a post-election opening in dialogue between America and Iran has so far shaped the West's cautious response to the crisis. Iran has been subjected to UN sanctions after its nuclear programme violated safeguards against weapons research.

"There's only a certain window of opportunity if they want to get Iran to stop its nuclear programme and all the time this situation is evolving that window of opportunity gets smaller," said Clement Therme, an analyst at the French Institute of International Relations.